The present invention relates to a new and improved construction of apparatus for resistance welding the seams of can bodies or the like by means of electrode rolls or rollers.
During the welding of can bodies, typically formed of tin plate or sheet metal, in resistance welding machines which weld the seam of such can bodies by means of electrode rolls or rollers and normally employ centering and clamping devices in order to ensure for the complete parallelism of the edges of the can bodies in the Z-rail serving as guide means, there exists the disadvantage that the squeezing together of the overlap seam produces a relatively intensive wear of the welding roll due to the formation of notches or grooves thereat. Therefore there is frequently required a post-machining of the bronze material of the electrode rolls, in order to ensure for the requisite quality of the overlap welding seam. This post-machining work is associated with extremely high material losses.
In order to reduce this post-machining work, there has been proposed according to Swiss Pat. No. 429,982 shifting of the sheet metal guide means, i.e. the Z-rail transversely with respect to the lengthwise axis thereof. Due to these measures there are shifted the contact locations of the overlapping edges of the can body at the electrode rollers, whereby there can be prevented the formation of grooves or notches.
In welding machines where the Z-rail simultaneously assumes the function of the supporting structure for the upper electrode roller, it is not possible to use the previously described apparatus.
Furthermore, it is known from the aforementioned Swiss Pat. No. 429,982 to periodically somewhat axially displace the electrode rollers or rolls by means of handwheels mounted at the shafts or axles of the electrode rollers.
This displacement mechanism is only suitable for use with slowly operating welding machines having low production rates.